The field of this invention relates to a composition comprising a blend of a polyarylate with a poly(p-methylenebenzoate) (PPMB), a poly(m-methylenebenzoate) (PMMB), or mixtures thereof. These compositions have improved processability relative to the polyarylate and improved weatherability relative to the PPMB or PMMB. The compositions of this invention comprise a polyarylate derived from a dihydric phenol and an aromatic dicarboxylic acid, and PPMB, or PMMB, or mixtures thereof. The thermoplastic blends can be easily molded by injection or vacuum forming techniques or by extrusion to form a large variety of useful shaped articles.
Polyarylates are aromatic polyesters derived from a dihydric phenol, particularly 2,2-bis(4-hydroxyphenyl)propane (also identified as Bisphenol-A) and an aromatic dicarboxylic acid, particularly mixtures of terephthalic and isophthalic acids.
Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They have a high, continuous use temperature of about 130.degree. C., and good unnotched toughness, with a pendulum impact value of greater than 300 ft.-lbs./in..sup.3. Additionally, polyarylates have inherent flammability and combustion resistance. The polyarylates have good color retention. They also have good processability which allows them to be molded into a variety of articles. However, processing of polyarylates is by injection molding or extrusion at temperatures greater than about 330.degree. C. These high processing temperatures can require the use of special equipment, such as heated molds. Thus, it is desirable to improve the processability of polyarylates.
Poly(p- and m-methylenebenzoate) polyesters suitable for manufacture of useful textile fibers are derivatives of p- and m-hydroxymethylbenzoic acid, the methylester and polymers disclosed in U.S. Pat. No. 4,130,719, which is incorporated herein by reference. A similar procedure can be used to prepare ethyl and higher analogues.
Poly(p- and m-methylenebenzoate) polyesters are high molecular weight polymers having vastly improved properties over polymers previously known. This particular polymer is a normally amorphous polymer, has excellent impact strength and solvent resistance, and is characterized by an inherent viscosity from 0.4 to 2.0 dl/g. It is particularly useful as an engineering plastic but can be used in other applications as well.
It has been unexpectedly found that the addition of PPMB or PMMB, or mixtures thereof, to a polyarylate improves the processability of the polyarylate in that it increases melt flow. This allows lowering of the melt temperature and of the mold temperature which allows for faster cycle time in injection molding.
Polyarylates have good weatherability, i.e., the retain their mechanical properties after exposure to conditions to ultraviolet light and moisture. In contrast, the weatherability of poly(p- and m-methylenebenzoate) polymers is generally poor since they lose their impact properties upon exposure to ultraviolet light. Use of typical ultraviolet stabilizers only marginally improves the stability of PPMB, PMMB, or mixtures thereof. Therefore, it was unexpected that the addition of a polyarylate, even in small amounts, to PPMB, PMMB, or mixtures thereof results in a composition having improved weatherability.
Additionally, polymer blends, even those comprising transparent polymeric materials, usually yield an opaque composition due to incompatibility of the components. The blends of polyarylate and PPMB, PMMB, or mixtures thereof when combined in all proportions yield transparent compositions which exhibit a single glass transition temperature and can be molded into useful articles.
British Pat. No. 1,002,545 describes a blend wherein one of the components is a polyester of terephthalic acid and one or more aliphatic diols, and the other component is a polyarylate of 2,2-di(4-hydroxyphenyl)propane and terephthalic and isophthalic acid, the ratio of terephthalate residues to isophthalate residues in the copolyester ranging from 90:10 to 10:90.
The British patent describes that the blend of the polyester and polyarylate provides an easily moldable polymer blend without the disadvantages attendant when molding each of the two components alone. The examples of the British patent describe a blend of poly(ethyleneterephthalate) and a polyarylate of 2,2-di(4-hydroxyphenyl)propane and isophthalic and terephthalic acid. The British patent states that the aliphatic diol from which the polyester is derived may be cycloaliphatic, such as 1,4-di(hydroxymethyl)cyclohexane.
U.S. Pat. No. 4,246,381 to Robeson describes a blend of copolyester derived from a cyclohexanedimethanol, and alkylene glycol and an aromatic dicarboxylic acid and a polyarylate derived from a dihydric phenol and an aromatic dicarboxylic acid. The blend is described as having improved processability relative to the polyarylate and improved weatherability, impact properties and heat distortion temperature relative to the copolyester.
U.S. Pat. No. 4,250,279 to Robeson, et al., describes molding compositions of blends of a polyarylate derived from a dihydric phenol and an aromatic dicarboxylic acid, and a polyetherimide. The blends are described as having improved environmental stress crack resistance relative to the polyarylate and improved impact strength relative to the polyetherimide. The compositions containing polyetherimide and polyarylate are described as having excellent mechanical compatibility and excellent mechanical properties.
British Pat. No. 1,002,545 and U.S. Pat. Nos. 4,246,381 and 4,250,279 do not suggest that easily moldable blends of a polyarylate of a dihydric phenol and an aromatic acid can be obtained by the addition of a poly(p-methylenebenzoate) polyester or a poly(m-methylenebenzoate) polyester or that the weatherability of poly(methylenebenzoate) polymers is improved by the addition of a polyarylate. British Pat. No. 1,002,545 does not suggest the blend of copolyesters and polyarylate has different impact properties than either component. U.S. Pat. No. 4,246,381 teaches that the impact strength of the copolyester is improved by the addition of polyarylate. In contrast, the tensile impact strength of poly(p-methylenebenzoate) and poly(m-methylenebenzoate) is decreased by the addition of polyarylate.